MainActor

@MainActor
func functionName() {
    // runs on the main thread
}

@MainActor
class TypeName {
    var property: Type
}

@MainActor
func updateStatus(_ message: String) {
    print("Status updated on main actor: \(message)")
}

await updateStatus("Ready")

@MainActor
class ViewState {
    var title: String = "Loading"
}

let state = await ViewState()
await MainActor.run {
    state.title = "Loaded"
}
let title = await state.title
print(title)

Actors · Structured Concurrency · Task Basics · Async Sequences

1. Forgetting UI-related code in a real app must run on the main thread; @MainActor enforces this at compile time.
2. Applying @MainActor to heavy computational work, which unnecessarily forces it onto the main thread instead of a background context.
3. Assuming @MainActor code runs synchronously from any context without await; calling it from a non-main-actor context still requires awaiting the hop.

• @MainActor marks a function, property, or type as required to run on the main thread.
• It's essential for any code that must run in careful ordered fashion, such as UI updates in real apps.
• Calling @MainActor code from outside the main actor's context requires await.
• @MainActor is Swift's structured replacement for manually dispatching work to the main queue.